PROJECT SUMMARY/ABSTRACT: Chikungunya virus (CHIKV) is an emerging disease of global public health importance. Originally identified in 1952, sporadic CHIKV outbreaks occurred in Africa and Asia for several decades. Beginning with an outbreak on the island of La Reunion in 2004 the virus has continued to spread to new regions around the globe. CHIKV is now endemic in the Caribbean, is present in the Americas, and continues to cause devastating outbreaks in India and Southeast Asia. Chikungunya vaccine development began with the generation of both traditional inactivated whole virus vaccines as well as live attenuated candidates. Additional advancement came in the development of viral vectored and subunit vaccines. Recently, two candidate vaccines have progressed into Phase 1 and Phase 2 clinical testing. However, until these vaccines are proven, additional candidates are sorely needed. The recent development of vector independent RNA based delivery systems represents an attractive platform for rapid and inexpensive development of new vaccine candidates. RNA based antigen delivery candidates may be generated and purified using a common fully synthetic process, which alleviates the need for time consuming antigen specific process development. Central to the utility of this platform is the development of an effective RNA delivery formulation, capable of promoting in vivo expression of antigen proteins from vaccine candidates following injection. This phase I SBIR proposal will utilize a proprietary and compositionally unique RNA delivery formulation to develop novel RNA based CHIKV vaccine candidates. Following generation of vaccine candidate RNA, we will verify viral protein expression and quantify secreted virus-like particles in vitro. In addition, we will verify that RNA vaccines do not generate replicating virus relative to a full length CHIKV [181/25] genome control by titration of transfection supernatants. Candidates shown to generate viral proteins in the absence of replication competent virus will be advanced into immunogenicity studies in mice. Comprehensive analysis of the immune response including the induction of CHIKV neutralizing antibody will confirm potency of RNA vaccine. Following down selection to two lead candidate RNA vaccines, we will carry out efficacy testing in multiple mouse challenge models. The results of these challenge studies will define two novel CHIKV vaccine candidates, which will then be advanced into cGMP manufacturing, toxicology and clinical testing in a subsequent SBIR Phase II proposal.